Katryne wrote:

Hello Gattonero,
I do not ganrantee I give the right soluce, but I want to convey a piece of my experience with sites in subdirectories, not specially a Piwigo.
I met this kind of issue when using subdirectory instead of subdomain : the cookies of the main site get mixed with the cookies of the site in subdirectory. And it's problematic in particular with loging. Everything worked correctly when I passed the site to a subdomain of the kind : https://piwigo.domain.org

I've hoped not to read this :D ...but It's a hosting with no possibilities to create subdomains (I think) so i'm doomed and I've to find another solution :(
Thank you!